Measurement of the 21Ne Zeeman frequency shift due to Rb-21Ne collisions

Using a 21Ne-3He Zeeman maser, we compared the frequency shift of the 21Ne nuclear Zeeman resonance induced by polarized Rb vapor to the shift induced in the 3He nuclear Zeeman resonance. The 3He-Rb shift has recently been measured with high precision [M.V. Romalis and G.D. Cates, Phys. Rev. A 58, 3004 (1998)], permitting the conversion of our differential measurement to an absolute value for the 21Ne-Rb shift. We report a value of κ21=32.0±2.9 for the Rb-21Ne contact shift enhancement factor at a temperature of approximately 128 deg. C. We also propose high-precision differential contact shift measurements, the absolute accuracy of which could be limited by the error in the 3He contact shift